Page:The Journal of geology (IA journalofgeology21894univers).pdf/288
able as yet to offer any satisfactory explanation," can be, since it terminates before it reaches the point of scicula, nothing else than that portion of the virgula which lies in the wall of the scicula.
Tornquist nowhere says that the described species are monoprionidian, but this can be clearly seen in the figures 39-41 of Cephalograptus cometa, Gein., and if those just cited are compared with my own, there can be no doubt that the species above mentioned are also monoprionidian.
It is particularly interesting to note that the presence of a longitudinal septum does not depend on the diprionidian character of the Diplograptidæ as generally accepted.
Explanation of Plate.
The figures have been drawn about twice the size of the scale, with Zeiss and Abbe's drawing apparatus. The shading was obtained by still greater enlargement, and by various accessories to the microscope. The given scale does not apply to figure 10.
- Fig. 1. Young scicula; dorsal side.×37.
- Figs. 2-3. Adult scicula; front view. The thecæ are removed.37-1.
- Fig. 4. Form and place of the first theca and the perforation from which the second will come; front view.×37.
- Fig. 5. The same; dorsal view.×37.
- Fig. 6. The first theca with three spines, two of which are united by a thin skin.×37.
- Fig. 7. Form and position of the second and third thecæ; front view.×37.
- Fig. 8. Form and position of the fourth theca and imbedded scicula.×37.
- Fig. 9. Incorporation of the scicula in the hydrosoma.×37.
- Fig. 10. Distal portion. The transparency partially made use of. The virgula is wholly free.×13.
- Figs. 11-12. Attachment of the proximal edges of the partitions to the virgula.×37.
The material is in the collection of the Geological Institute at Upsala.
Carl Wiman.